As is well known, polymers are molecules containing one or more chains, each containing multiple copies of one or more constitutional units. An example of a common polymer is polystyrene
where n is an integer, typically an integer of 10 or more, more typically on the order of 10's, 100's, 1000's or even more, in which the constitutional units in the chain correspond to styrene monomers:
(i.e., they originate from, or have the appearance of originating from, the polymerization of styrene monomers, in this case the addition polymerization of styrene monomers).
Copolymers are polymers that contain at least two dissimilar constitutional units. Copolymers are an important class of polymers and have numerous commercial applications. For instance, their unique properties, whether in pure form, in blends, in melts, in solutions, etc., lead to their use in a wide range of products, for example, as compatibilizers, adhesives, dispersants, and so forth. Because each copolymer has its own unique properties, there is continuing demand for novel copolymers, which can be used in products such as those above.
It is well known that living polymerization (i.e., polymerization proceeding in the practical absence of chain transfer to monomer and irreversible termination) is a very useful method for designing polymer structures. One of the most useful features of living polymerizations is the ability to prepare block copolymers. Living cationic sequential block copolymerization is generally recognized as one of the simplest and most convenient methods to provide well-defined block copolymers with high structural integrity.
Linear-, star-, and arborescent-block copolymers with a rubbery polyisobutylene (PIB) center block and glassy end blocks are useful thermoplastic elastomers, exhibiting excellent properties such as thermal and oxidative stability and biocompatibility. To date a large number of these block copolymers with polystyrene, poly(p-methylstyrene), poly(p-tert-butylstyrene), poly(p-chlorostyrene), poly(p-fluorostyrene), poly(α-methylstyrene) and polyindene as end blocks have been prepared.
All of the above thermoplastic elastomers contain a hydrophobic end blocks. Some applications, however, require block copolymers where the end blocks are hydrophilic. The ability to tune the overall hydrophilicity of the block copolymer would provide a wide range of useful products.
Although the living homopolymerization and copolymerization of p-hydroxystyrene and p-tert-butoxystyrene has been reported with BF3.OEt2 coinitiator in the presence of a large amount of water in MeCN/CH2Cl2 solvent at 0° C., see Satoh, Kotaro; Kamigaito, Masami; and Sawamoto, Mitsuo, Department of Polymer Chemistry Graduate School of Engineering, Kyoto University, Kyoto, Japan, Macromolecules (2000), 33(16), 5830, this system is not applicable for the living polymerization of isobutylene. Cationic living polymerization of p-tert-butoxystyrene has also been reported in aqueous emulsion polymerization and by the HI/ZnI2 initiating system in toluene or CH2Cl2. Higashimura, T.; Kojima, K.; Sawamoto, M., Makromolekulare Chemie, Supplement 1989, 15, 127. The HI/ZnI2 initiating system, however, is inactive for the polymerization of isobutylene (IB).